On the market today, there is an increasing demand for packages for beverage and liquid food of the type that are single-use disposable plastic pouches, preferably at least partly, at some portion of the package, transparent to display the contents to the consumer when exposed on the shelf, e.g. in the food store. Most commonly such packages are provided with a straw for direct drinking or a pull-tab for opening and pouring of the contents. Such packages do not have the advantage of having the dimension and grip stability of the more common paperboard packaging laminate drink packages of the Tetra Brik®-type. However, they have the image of a more positive environmental profile in many countries, with the argument that the amount of used packaging material as well as the volume of the emptied package is very small and because it may be recyclable with other similar flexible plastic items. Furthermore, the traditional Tetra Brik®-type packages have an oxygen barrier layer of aluminium foil, which in some countries is less desirable and which also makes a transparent package impossible.
In the high-speed, continuous packaging processes well known for the paperboard packages of the Tetra Brik®-type, a web of the packaging laminate is continuously formed into a tube, filled with contents and sealed off to pillow-shaped packaging containers by a simultaneous heat sealing and cutting operation. The pillow-shaped packaging container is then normally foldformed into a parallellepipedic packaging container. The main advantage of this continuous tube-forming, filling and sealing packaging process concept is that the web may be sterilized continuously just before tube-forming, thus providing for the possibility of an aseptic packaging process, i.e. a process wherein the liquid content to be filled as well as the packaging material itself are reduced from bacteria and the filled packaging container is produced under clean circumstances such that the filled package may be stored for a long time even at ambient temperature, without the risk of growth of microorganisms in the filled product. An important factor for long-term storage is of course also the gas barrier properties of the filled and sealed packaging container, which in turn is highly dependent on the gas barrier properties of the packaging laminate itself but also on the qualities of the seals and of the opening arrangement of the final package. An other important advantage of the Tetra Brik®-type packaging process is, as stated above, the possibility of continuous high-speed packaging, which has considerable impact on cost efficiency. The pouch-type drink packages available today on the market, are however, typically manufactured by other non-aseptic, more complex and expensive processes of less continuous character.
In the prior art it is also known to apply gas barrier coatings of SiOx onto a substrate by means of plasma enhanced chemical vapour deposition (PECVD). The advantages with a SiOx gas barrier layer compared to other gas barrier materials are firstly that it has a positive environmental profile, secondly, that it is not affected when in contact with surrounding moisture or liquid, it is transparent and since it is applied in very thin layers, also flexible and resistant to cracking when bent or folded.
It is known from EP-A-385054 to laminate two gas barrier layers of a silicon compound, such as silicon dioxide, facing each other, by means of an intermediate binder layer. This document, however, is silent on the stiffness properties of the laminate and does not describe a thicker or stiffer intermediate layer. Moreover, the silicon dioxide (SiO2) layers described are very different from the PECVD-coated layers of SiOx intended according to this invention.
There is thus a need for a thin, transparent, gas-tight, metalfoil-free packaging laminate having suitable properties for an aseptic, continuous highspeed packaging process similar to the Tetra Brik Aseptic® packaging process.
An important factor in such a process is the stiffness and stability of the packaging laminate. If the laminate web is too flexible and easy to displace in the high-speed tube-forming operation, the process will not be able to run safely and continuously. On the other hand, if the packaging laminate is too thick in order to obtain the required stiffness, it may be difficult to manage in the fold-forming operation. Moreover and naturally, the cost-efficiency of the material itself wilt be reduced with increasing thickness. The pouch-type drink packages available today on the market often have a laminated structure including a single gas barrier layer of, for example, an ethylene vinyl alcohol polymer (EVOH), and do not have the requirements on stiffness properties according to the present invention.
It is therefore an object of the present invention to provide a packaging laminate that alleviates the above discussed disadvantages and problems.
It is an object of the present invention to provide a transparent packaging laminate, having gas barrier properties suitable for aseptic packaging and long-term storage, as well as sufficient bending stiffness to be suitable for continuous, high speed packaging of liquid foods by means of a continuous tube-forming process.
It is a further object of the invention to provide a packaging laminate having the required stiffness but being sufficiently thin for foldforming of the package at at least one end of the package.
The invention is also directed to a packaging container filled with beverage or liquid food produced from the packaging laminate of the invention as well as to a method of manufacturing of the laminated packaging material of the invention.